Of the 81 trisomy 21 cases, the researchers classified all 81 as high risk for trisomy 21. There was one false positive in 2,888 normal cases, for an overall sensitivity of 100% and a 0.03% false-positive rate. Thirty-seven of the 38 cases of trisomy 18 were classified as high risk and two false positives were seen among the 2,888 normal cases, for a sensitivity of 97.4% and a false-positive rate 0.07%.

"Chromosome-selective sequencing of cfDNA and application of an individualized risk algorithm is effective in the detection of fetal trisomy 21 and trisomy 18," the authors write.

Several authors are employed by or have other financial ties to Ariosa Diagnostics, which funded the study.